1. Field of the Invention
This invention relates generally to data communications systems and methods. In particular, the present invention relates to a packet data switch controller suitable for implementation in a communications satellite.
2. Description of Related Art
Switched packet data communications systems and methods are well known in the art. Perhaps the most prevalent examples of switched packet data communications systems are those utilizing the Asynchronous Transfer Mode (ATM) network protocol developed to efficiently move information at a faster rate. The networks of switched packet data communications systems include a number of packet switches of otherwise minimum functionality which move user information encapsulated into packets (sometimes referred to as cells) from an input port to an output port. In addition to the user (or payload) data, these packets have a header containing information to be used inside the network for routing, error correction, flow control, etc. For example, the packets in an ATM network are defined as having 53 bytes composed of a 5 byte header and 48 byte payload information.
The general architecture of a conventional packet switch 100 in such a network is shown in FIG. 1. It consists of a number of input interface modules 1011 to 101n, a switching module 102, a number of output interface modules 1031 to 103n, and a switch manager 104. Each input interface module 1011 to 101n includes a physical interface to an optic fiber or a cable, such as a coaxial cable commonly used in CATV systems, of the network. Each input interface module 1011 to 101n performs validation and translation of virtual channel identifier (VCI) and virtual path identifier (VPI), a header error control (HEC) check, statistics collection, conforming traffic validation, and general traffic shaping and policing. Switching module 102 routes the packets from each input interface module 1011 to 101n to the correct output port, replicates multicast packets, discards packets depending on traffic congestion, and performs priority queuing of packets. Each input interface module 1031 to 103n also includes a physical interface to an optic fiber or a cable, such as a coaxial cable commonly used in CATV systems, of the network and also performs statistics collection. Switch manager 104 performs network management and connection management.
Although not shown in FIG. 1, conventional packet switch 100 may utilize a number of general purpose processors. These processors are usually tightly coupled in a specific configuration, with a connection path between the general purpose processors fixed by hardware, and having one operating system performing unified management for the configuration of processors. However, the general purpose processors may be loosely coupled to one another and operated by a distributed real-time operating system in conjunction with embedded firmware. In such a loosely coupled system, if one processor fails, the system must be rebooted in order to have the failed processor replaced with another processor. The necessity of rebooting the system in order to implement fault correction is a major disadvantage in a communications satellite responsible for providing switching for a large amount of data packets.
Packet switch 100 is usually provided as a discrete element in a terrestial based network. As such, there is usually easy access to the packet switch in the event of a fault or malfunction, and in order to perform maintenance, diagnostic tests, or software update installations. Packet switch 100 is thus generally unacceptable for installation in extremely remote locations and the network thus has geographical limitations, such as those imposed by large bodies of water and by space.
Remote locations also present other obstacles. For example, in a space-based communications satellite, it is customary to provide a control processor to manage the overall operation of the processing suite and to provide a central point of interaction for reception of, reaction to, and implementation of control directives from the ground, collection and gathering of statistics, formatting and sending of reports on processing activity, etc. Since packet switch 100 is a discrete element in a terrestial communications system, it is usually designed independently without taking into consideration the other elements of the network in which it is installed and is unsuitable for use in a communications satellite. For example, during a long period of operation in orbit, several processors and other elements of a communications satellite may fail. Although embedded firmware in conjunction with real-time distributed operating system provides a limited amount of software adaptability in those systems with loosely coupled processors as described above, there is a need for a multiprocessor operating and application software structure for a packet switch in a communications satellite that efficiently meets the operational performance requirements of the and provides a framework for more operational robustness, fault tolerance and reliability.
It is an object of the following preferred embodiments of the invention to provide a global packet data communications system. In particular, the preferred embodiments preferably include packet switches installed on board satellites located in a geosynchronous, medium earth, or low earth orbit in space. The satellites of these embodiments are preferably capable of operating in different communications applications.
As part of the preferred embodiments, it is a particular object to provide a fast cell/packet switch having a general software architecture particularly well suited for the above objects. The software architecture of the fast cell/packet switch is preferably flexible so as to be able to satisfy the communications desires of different users. In particular, the switch must be able to operate at speeds higher than conventional packet switches and must be able to implement fault correction without the need for rebooting.
A real-time control processor is used in the communications satellite of the preferred embodiments. In addition to managing the overall operation of the processing subsystem, it also provides a packet switch controller performing switch configuration and management, and dissemination functions. This real-time control processor, including the packet switch controller, must efficiently achieve the throughput required of the switch control function.
Throughput efficiency is achieved through optimization of the distribution of layered software control functions and application software to each one of multiple general processors (GPs) and digital signal processors (DSPs). In particular, there is layering of: (a) firmware optimized for specific hardware control or I/O data movement functions; (b) a real-time operating system for general purpose processing; (c) software executives optimized for DSP and embedded I/O control functions; and (d) application software distributed and optimized to each DSP and GP. This feature allows the combination of GPs and DSPs for efficient distribution of software control functions. In the event of a failure of any one processor, tasks can be redistributed or a switch can be made to a different processor.
A preferred application of the present invention is in a wideband satellite communications system transmitting payload data over a number of different frequency channels at extremely high data rates. The communications satellite of such a system has significant processing requirements, such as demodulation and channelization of the wideband signal into narrowband channels, in addition to the packet switch controller. The system may be a xe2x80x9csecurexe2x80x9d frequency-hopped communications system in which reception of the transmitted waveform by the communications satellite requires dehopping and/or frequency hopping of the data transmitted by the communications satellite.
In addition to the foregoing summary, a better understanding of the preferred embodiments will become apparent from the following detailed description of the preferred embodiments when read in connection with the accompanying drawings. While the foregoing and following written and illustrated disclosure focuses on disclosing preferred embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. In particular, several elements and features of the preferred embodiments are not essential for implementation of the invention. The spirit and scope of the present invention is limited only by the terms of the claims in the patent issuing from this application and not by the preferred embodiments.